For example, a driving device as a semiconductor device for a switching element turns on and off the switching element by controlling a voltage applied to a control terminal of the switching element. In this case, a main factor for determining an on time and an off time of the switching element relates to a charging and discharging time according to a parasitic capacitance.
The charging time of the parasitic capacitance is determined by a magnitude of current to flow into a control terminal of the switching element from a driving circuit. Accordingly, in order to shorten the charging time, the current to flow into the control terminal is increased. In view of this technique, an applied voltage of the control terminal of the switching element is, for example, forcibly controlled to be closer to a power source voltage.
Thus, the driving circuit according to the prior art provides a high speed switching operation by increasing the current flowing through the parasitic capacitor from the control terminal of the switching element. However, in this case, it is necessary to increase a current supply capacity of the driving circuit. In order to solve this difficulty, JP-A-2008-235997 describes that an inductor is arranged around a current path, through which a main current of the switching element flows. An induced electromotive force generated at the inductor is overlapped on an applied voltage of the control terminal of the switching element. This operation provides a high speed operation of the switching element without increasing the current supply capacity of the driving circuit.
In order to put the technique in JP-A-2008-235997 into practical use, an arrangement of the inductor with respect to the main current path is a point of the technique. In JP-A-2008-235997, a ferrite core having a ring shape and a coil wound around the core are used. In this case, the core has the ring shape, and the core is arranged to be spaced apart from a lead. Therefore, it is difficult to fix the coil.